1. Field of the Invention
Embodiments of the present invention generally relate to a heat-assisted magnetic recording (HAMR) head.
2. Description of the Related Art
Higher storage bit densities in magnetic media used in disk drives have reduced the size (volume) of magnetic bits to the point where the magnetic bit dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, the data stored within the cells may not be thermally stable. That is, random thermal fluctuations at ambient temperatures may be sufficient to erase data. This state is described as the superparamagnetic limit, which determines the maximum theoretical storage density for a given magnetic media. This limit may be raised by increasing the coercivity of the magnetic media or by lowering the temperature. Lowering the temperature may not always be practical when designing hard disk drives for commercial and consumer use. Raising the coercivity, on the other hand, requires write heads that incorporate higher magnetic moment materials, or techniques such as perpendicular recording (or both).
One additional solution has been proposed, which uses heat to lower the effective coercivity of a localized region on the magnetic media surface and writes data within this heated region. The data state becomes “fixed” once the media cools to ambient temperatures. This technique is broadly referred to as “thermally assisted (magnetic) recording” (TAR or TAMR), “energy assisted magnetic recording” (EAMR), or HAMR which are used interchangeably herein. It can be applied to longitudinal and perpendicular recording systems as well as “bit patterned media”. Heating of the media surface has been accomplished by a number of techniques such as focused laser beams or near-field optical sources.
HAMR contain two optical components: a microphotonic spot-size converter (SSC) and a near-field transducer (NFT). SSCs transform the output of an external light source, such as a semiconductor laser diode (LD) into a well-confined guided mode that delivers light into the NFT. The NFT is a plasmonic nanoantenna that focuses the light further into an ultra-small spotsize, which is far beyond the diffraction limit, needed for high density magnetic recording. While there are many optical systems capable of performing the transformation, one of the simplest and most efficient realizations involves a taper SSC. Taper SSCs are used to overcome the significant modal mismatch between the free-space beams (or optical fiber modes) and the on-chip photonic components. Tapered SSCs are designed for a particular incident LD input to minimize optical conversion losses. However, even with a tapered SSC, conversion efficiency for the light is less than 40 percent.
Therefore, there is a need in the art for an improved SSC for HAMR heads.